This application is related to U.S. application Ser. Nos. 13/444,956; 13/444,972, now abandoned; U.S. application Ser. Nos. 13/444,906; 13/444,918; 13/444,929; 13/444,948; 13/444,986; and 13/445,088, now granted as U.S. Pat. No. 8,539,749, all of which were filed concurrently herewith, and which are fully incorporated by reference herein and made a part thereof.
This present application relates generally to combustion turbine engines and systems related thereto. More specifically, but not by way of limitation, the present application relates to methods, systems and/or apparatus for achieving operation at the stoichiometric point and extracting a working fluid having desired characteristics within various types of combustion turbine systems having exhaust gas recirculation.
Oxidant-fuel ratio is the mass ratio of oxidant, typically air, to fuel present in an internal combustion engine. As one of ordinary skill in the art will appreciate, if just enough oxidant is provided to completely burn all of the fuel, a stoichiometric ratio of 1 is achieved (which may be referred to herein as “operating at the stoichiometric point” or “stoichiometric point operation”). In combustion turbine systems, it will be appreciated that combustion at the stoichiometric point may be desirable for several reasons, including lowering emissions levels as well as performance tuning reasons. In addition, by definition, stoichiometric point operation may be used to provide an exhaust (which, in the case of a system that includes exhaust recirculation, may be referred to generally as “working fluid”) that is substantially free of oxygen and unspent fuel. More specifically, when operating at the stoichiometric point, the working fluid flowing through certain sections of the recirculation circuit or loop may consists of significantly high levels of carbon dioxide and nitrogen, which, when fed into an air separation unit, may yield substantially pure streams of these gases.
As one of ordinary skill in the art will appreciate, producing gas streams of carbon dioxide and nitrogen in this manner has economic value. For example, the sequestration of carbon dioxide has potential value given current environmental concerns relating to emission of this gas. In addition, pure gas streams of carbon dioxide and nitrogen are useful in many industrial applications. Also, carbon dioxide may be injected into the ground for enhanced oil recovery. As a result, novel power plant system configurations and/or control methods that provide efficient methods by which stoichiometric point operation may be achieved would be useful and valuable. This would be particularly true if novel systems and methods provided effective ways by which existing power plants using reheat and exhaust gas recirculation could achieve improved operation via relatively minor, cost-effective modifications. Other advantages to the systems and methods of the present invention will become apparent to one of ordinary skill in the art given the description of several exemplary embodiments that is provided below.